Liquid crystal displays (LCDs) are commonly used as display devices for compact electronic apparatuses because of their capability of displaying images with good quality while using little power. However, the liquid crystals in an LCD do not emit any light themselves. The liquid crystals have to be lit up by a light source so as to clearly and sharply display text and images. Usually, a backlight device is employed as such a light source.
Typically, a backlight device comprises a plurality of light emitting diodes (LEDs), which are arranged in the form of a matrix. An LED can be characterized in general by physical characteristics such as luminous intensity, which can be used to describe the brightness of an LED and is represented by Iv in unit of mcd (millicandela), wavelength, which can be used to describe the color of an LED and is represented by Wd in unit of nm (nanometer), and positive voltage, which can be used to describe the operating range of an LED and is represented by Vf in unit of V. Luminous flux, in unit of lm (lumen), can also be used to describe the brightness of an LED. Ideally, if the plurality of light emitting diodes were identical to each other in terms of these physical characteristics, a corresponding backlight device would generate light with uniform brightness and desired colorfulness.
However, in reality, LEDs produced in industrial scale do not have same or identical physical characteristics; instead, they have a distribution for each of the characteristics. Table I shows specifications of a set of LEDs (2715 in total) that were produced by a manufacturer. As one can see from Table I, for examples, in Bin No. 3,
TABLE ISpecifications of a Set of LEDs2220JT3-RGB-AUO12K(950425)RedGreenBlueOutputBinIvWdVfIvWdVfIvWdVfQty102596~625620~6252~2.21033~1095525~5303.0~3.2186~200455~4603.0~3.213596~625620~6252~2.21033~1095525~5303.0~3.2186~200455~4603.2~3.444596~625620~6252~2.21033~1095525~5303.0~3.2200~216455~4603.0~3.205596~625620~6252~2.21033~1095525~5303.0~3.2200~216455~4603.2~3.436596~625620~6252~2.21033~1095525~5303.0~3.2216~233455~4603.0~3.207596~625620~6252~2.21033~1095525~5303.0~3.2216~233455~4603.2~3.418596~625620~6252~2.21033~1095525~5303.2~3.4186~200455~4603.0~3.21589596~625620~6252~2.21033~1095525~5303.2~3.4186~200455~4603.2~3.440010596~625620~6252~2.21033~1095525~5303.2~3.4200~216455~4603.0~3.24511596~625620~6252~2.21033~1095525~5303.2~3.4200~216455~4603.2~3.439912596~625620~6252~2.21033~1095525~5303.2~3.4216~233455~4603.0~3.2013596~625620~6252~2.21033~1095525~5303.2~3.4216~233455~4603.2~3.43114596~625620~6252~2.21095~1160525~5303.0~3.2186~200455~4603.0~3.2315596~625620~6252~2.21095~1160525~5303.0~3.2186~200455~4603.2~3.4216596~625620~6252~2.21095~1160525~5303.0~3.2200~216455~4603.0~3.2417596~625620~6252~2.21095~1160525~5303.0~3.2200~216455~4603.2~3.4918596~625620~6252~2.21095~1160525~5303.0~3.2216~233455~4603.0~3.2019596~625620~6252~2.21095~1160525~5303.0~3.2216~233455~4603.2~3.4220596~625620~6252~2.21095~1160525~5303.2~3.4186~200455~4603.0~3.239921596~625620~6252~2.21095~1160525~5303.2~3.4186~200455~4603.2~3.445422596~625620~6252~2.21095~1160525~5303.2~3.4200~216455~4603.0~3.217123596~625620~6252~2.21095~1160525~5303.2~3.4200~216455~4603.2~3.456324596~625620~6252~2.21095~1160525~5303.2~3.4216~233455~4603.0~3.266there are four (4) LEDs that can emit red light, green light or blue light, where for a red light emitting LED, Iv is in the range of 596-625 mcd, Wd is in the range of 620-625 nm, and Vf is in the range of 2-2.2 V, for a green light emitting LED, Iv is in the range of 1,033-1,095 mcd, Wd is in the range of 525-530 nm, and Vf is in the range of 3.0-3.2 V, and for a blue light emitting LED, Iv is in the range of 186-200 mcd, Wd is in the range of 455-460 nm, and Vf is in the range of 3.2-3.4 V, respectively. In Bin No. 20, there are three hundred ninety-nine (399) LEDs that can emit red light, green light or blue light, where for a red light emitting LED, Iv is in the range of 596-625 mcd, Wd is in the range of 620-625 nm, and Vf is in the range of 2-2.2 V, for a green light emitting LED, Iv is in the range of 1,095-1,160 mcd, Wd is in the range of 525-530 nm, and Vf is in the range of 3.2-3.4 V, and for a blue light emitting LED, Iv is in the range of 186-200 mcd, Wd is in the range of 455-460 nm, and Vf is in the range of 3.0-3.2 V, respectively. Thus, LEDs as produced have an inherent distribution for each of the characteristics, which lead to undesired nonuniform distribution of brightness and/or colorfulness of an LCD display when the LEDs are utilized in a backlight unit for that LCD display.
Making LEDs having same or identical physical characteristics, even if it is possible, requires better materials and tougher quality control, among other things, which further increases the cost of the backlight unit.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.